The present invention relates to a rotary disk type storage device such as a magnetic disk drive and a magnet-optical disk drive.
In a rotary disk type storage device such as a magnetic disk drive, one or more disk-like recording mediums are rotatably supported by drive means such as a spindle motor, an arm, which holds a read/write head (hereinafter simply referred to as a head), is supported pivotably in a plane almost parallel to a recording surface of the recording medium, and the arm is rotated by another drive means such as a voice coil motor to move the head to a desired position on the recording medium. These components are accommodated in a thin box-shaped casing.
Such a rotary disk type storage device is finding a widening range of applications in desk-top personal computers, notebook personal computers and audiovisual equipment. In this circumstance there is a growing demand for reducing the size, weight, noise and cost of the storage device.
For realizing lighter weight and reduced cost, it is often a conventional practice to form a box-like base casing by die-casting and a cover casing by stamping. In a small-diameter magnetic disk drive wherein magnetic disks are 2.5 inches or smaller in diameter, when reducing a thickness of the cover casing, it is typical to bend the periphery of a flat plate during stamping, because the flat plate cannot provide a sufficient rigidity.
In a magnetic disk drive, it has been known that vibrations due to rotation of a rotating magnetic disk and vibrations due to a seek operation for positioning the head by the actuator oscillate the base casing and cover casing thus generating noise. Particularly in a construction wherein a disk-shaped recording medium is secured to a free end of a shaft of the spindle motor, the recording medium is held in a cantilevered state. So, when some external force is applied to the recording medium, the shaft of the spindle motor swingingly rotates, generating vibrations.
To reduce these vibrations, measures have been taken to enhance the performance of a spindle motor, improve a spindle motor current control method, and improve an actuator control current. The vibrations, however, are difficult to eliminate completely.
Therefore, to suppress vibrations of a cover casing, which has been considered the main source of noise, a variety of proposals have been made, including forming the entire cover from a vibration damping steel plate or, as disclosed in JP-11-232862A, attaching a vibration damping steel plate to the outside of the cover casing to absorb vibrations and thereby reduce noise.
However, it is contrary to reduction of the weight as well as cost to form the entire cover casing from a vibration damping steel plate so as to suppress vibrations of the cover casing that occur during the seek operation of the actuator, because such a cover increases in thickness. The method of attaching a vibration damping steel plate to the outer surface of the cover casing not only cannot produce as high a vibration absorbing effect as expected but it also leads to a cost increase.